Coated articles are known in the art for use in window applications such as insulating glass (IG) window units, vehicle windows, monolithic windows, and/or the like. In certain example instances, designers of coated articles often strive for a combination of high visible transmission, substantially neutral color, low emissivity (or emittance), low sheet resistance (Rs), low U-values in the context of IG window units, and/or low specific resistivity. High visible transmission and substantially neutral color may permit coated articles to be used in applications where these characteristics are desired such as in architectural or vehicle window applications, whereas low-emissivity (low-E), low sheet resistance, and low specific resistivity characteristics permit such coated articles to block significant amounts of IR radiation so as to reduce for example undesirable heating of vehicle or building interiors.
However, conventional coated articles are lacking with respect to one or more of: (i) thermal cycling performance, (ii) mechanical durability, (iii) ability to achieve good substantially neutral film side reflective coloration monolithically or more preferably in an insulating glass (IG) window unit, (iv) ability to realize a combination of good visible transmission (Tvis) and an excellent solar heat gain coefficient (SHGC) and low U-values for increasing or maximizing solar heat gain and reducing or minimizing heat loss of building interiors, and/or (v) ability to meet an Energy Rating (ER) of no less than 29.
In view of the above, it will be appreciated that there exists a need in the art for a coated article including a coating (e.g., in the context of an IG window unit) which has the ability to realize one or more of: (i) improved thermal cycling performance, (ii) improved mechanical durability, (iii) substantially neutral film side reflective coloration monolithically and/or more preferably in an insulating glass (IG) window unit, (iv) high Tvis and good SHGC, (v) low U-values, and/or (vi) an Energy Rating (ER) of no less than 29.
The Canadian Hydro-Quebec Energy Initiatives have asked for window product for residential applications with high solar heat gain, high visible light transmission, and good thermal insulation. In this respect, Zone C ER requires ER as high as 25, and Zone D requires ER no less than 29. Current conventional sputter-coated single Ag layer coatings in the market can meet some, but not all, requirements. In particular, they still need further energy rating improvement for residential applications in northern climates mainly due to not having a sufficiently high SHGC.
Certain example embodiments of this invention relate to a coated article including an infrared (IR) reflecting layer of a material such as silver or the like. In certain example embodiments, a layer comprising zinc oxide is provided under the IR reflecting layer in order to improve qualities thereof. In certain example embodiments, the coating is a single-silver type coating, and includes an overcoat including an uppermost layer of or including silicon nitride and a layer of or including tin oxide immediately under and contacting the silicon nitride based uppermost layer. In certain example embodiments, the thicknesses of the silicon nitride based uppermost layer and the tin oxide based layer of the overcoat are balanced (e.g., substantially equal, or equal plus/minus about 10%). It has surprisingly been found that balancing the thicknesses of the silicon nitride based layer and the adjacent tin oxide based layer results in a coating that has significantly improved thermal cycling performance and improved mechanical durability. In certain example embodiments, the silicon nitride based uppermost layer and the adjacent tin oxide based layer each have a thickness of at least about 90 angstroms (Å), more preferably at least about 120 Å, and still more preferably at least about 150 Å. For example, the silicon nitride based uppermost layer and the tin oxide based layer may each be from about 160-180 Å thick in certain example embodiments, so as to improve thermal cycling performance and durability of the coating. In certain example embodiments, the coating also has surprisingly good substantially neutral film side reflective coloration, monolithically or more preferably in an insulating glass (IG) window unit. In certain example embodiments, the thickness of the IR reflecting layer is adjusted to achieve a balance of low U-value and high SHGC for maximizing ER ratings.
In certain example embodiments, an IG window unit including the coating (e.g., on surface #3) has an SHGC value of no less than about 0.65, more preferably no less than about 0.68; and a visible transmission of at least about 68%, more preferably at least about 70%, 72%, or even at least about 74%. In certain example embodiments of this invention, the IG window unit can realize a combination of good visible transmission (Tvis) and an excellent solar heat gain coefficient (SHGC). For coatings according to example embodiments of this invention, a high SHGC is preferred because the coating is adapted for use in northern climates. The high SHGC desired for this coating is the opposite of low SHGC values desired for coatings for use in southern climates. In view of the above, it is possible to permit the coated article, such as an IG window unit for example, to realize improved properties such as one or more of a low U-value (e.g., U-value of no greater than about 0.33, 0.30 or 0.28), and/or an Energy Rating (ER) of no less than 25, more preferably no less than 29.
Additionally, in certain example embodiments, it has been found that the stress of the overcoat can be dramatically reduced by increasing inert gas flow rate (e.g., argon gas flow), and reducing nitrogen gas flow (N2 ml/kW) and cathode power during the sputter-deposition process of the overcoat. It has been surprisingly found that low overcoat stress is a significant factor contributing to good thermal cycling results.
In certain example embodiments, a layer comprising an oxide of Ni and/or Cr is provided between the tin oxide based layer and the Ag based IR reflecting layer, and the layer comprising Ni and/or Cr may be substoichiometric in order to provide improved adhesion to the overlying tin oxide based layer so as to improve durability. Coated articles herein may be used in the context of insulating glass (IG) window units, or in other suitable applications such as monolithic window applications, laminated windows, and/or the like.
In certain example embodiments of this invention, there is provided a coated article including a coating supported by a glass substrate, the coating comprising: at least one dielectric layer; a layer comprising zinc oxide over the at least one dielectric layer; an infrared (IR) reflecting layer comprising silver on the glass substrate, located over and directly contacting the layer comprising zinc oxide, wherein the coating includes only one IR reflecting layer; a layer comprising an oxide of Ni and/or Cr located over and directly contacting the IR reflecting layer comprising silver; an overcoat comprising a layer comprising tin oxide located over the oxide of Ni and/or Cr and a layer comprising silicon nitride located over and contacting the layer comprising tin oxide; and wherein, in the overcoat, the layer comprising tin oxide and the layer comprising silicon nitride have substantially equal thicknesses plus/minus 15% in order to improve thermal cycling performance and mechanical durability of the coating.
In other example embodiments of this invention, there is provided a method comprising: sputter-depositing at least one dielectric layer and at least one IR reflecting layer over at least the dielectric layer; sputter-depositing an overcoat on the glass substrate over at least the IR reflecting layer, the overcoat comprising a layer comprising tin oxide and a layer comprising silicon nitride located over and contacting the layer comprising tin oxide; and when sputter-depositing the layer comprising silicon nitride using a nitrogen gas flow of no greater than 450 sccm, using a cathode power of less than 50 kW, and using a ratio of nitrogen gas flow to cathode power (N2 ml/kW) of from about 6-10.
In yet another example embodiment of this invention, there is provided an IG window unit including a coating supported by a glass substrate, the coating from the glass substrate outwardly comprising: at least one dielectric layer; a layer comprising zinc oxide over the at least one dielectric layer; an infrared (IR) reflecting layer comprising silver on the glass substrate, located over and directly contacting the layer comprising zinc oxide, wherein the coating includes only one IR reflecting layer; a layer comprising an oxide of Ni and/or Cr located over and directly contacting the IR reflecting layer comprising silver; an overcoat comprising a layer comprising tin oxide located over the oxide of Ni and/or Cr and a layer comprising silicon nitride located over and contacting the layer comprising tin oxide; and wherein the IG unit has an SHGC value of at least 0.65, a visible transmission of at least 70%, and an Energy Rating of at least 25.